In a wireless local area network (Wireless Local Area Networks, WLAN for short) system, carrier sense and a channel reservation mechanism are used. When a channel is occupied by a site in a period of time, another site is not allowed to transmit data within this period of the time. FIG. 1 is a schematic diagram 1 of site communication. As shown in FIG. 1, a site C and a site B are within a coverage area of a site A. When the site A transmits data to the site B, the site C also receives a transmit signal of the site A. To avoid a conflict, the site C does not transmit data. Therefore, in the prior art, transmission efficiency of the system is not high.